1. Field of the Invention
The invention relates to a valve mechanism with a variable valve opening cross section and particularly to such a valve for use as an intake or an exhaust valve of an internal combustion engine.
2. Prior Art
In internal combustion engines used as driving engine for motor vehicles a fuel-air mixture is compressed and ignited in the work chamber. The energy produced is converted into mechanical work. It is known for air or the fuel-air mixture to be delivered to the work chamber via valves (intake or inlet valves), and for the products of combustion to be removed from the work chamber via valves (exhaust or outlet valves). For determining the efficiency of the engine, controlling these valves is of great significance. In particular, the gas exchange in the work chamber is controlled by way of controlling the valves.
In addition to camshaft control, it is also known to employ an electrohydraulic valve control. Electrohydraulic valve control offers the capability of variable or fully variable valve control, making it possible to optimize the gas exchange and thus to enhance the efficiency of the engine.
The electrohydraulic valve control includes a hydraulically actuatable control valve, whose control valve piston actuates a valve body of the inlet and outlet valves and leads to a valve seat (valve seat ring) (closure of the valve) or moves away from it (opening of the valve). The control valve can be actuated via a pressure control of a hydraulic medium. The pressure control is effected here via magnet valves incorporated into the hydraulic circuit. To achieve the most optimal possible gas exchanges, the highest possible switching speeds of the control valve are needed. As a result of these high switching speeds, the valve body of the inlet and outlet valves strikes the valve seat ring at high speed. The result is on the one hand noise, and on the other, the partners in the valve suffer relatively high wear.
European Patent Disclosure EP 0 455 761 B1, for instance, has a hydraulic valve control device for an internal combustion engine as its subject. The fundamental technological principle of this embodiment is to displace a motor valve by means of a controlled pressure of a hydraulic fluid. In this embodiment, it is provided that an electronic control unit triggers a magnet valve, which in turn controls the motion of a storage piston, by way of which the stroke of the motor valve is varied.
European Patent Disclosure EP 0 512 698 A1 describes an adjustable valve system for an internal combustion engine. This embodiment is one example of mechanical valve control via cams of a rotating camshaft.
U.S. Pat. No. 4,777,915 has an electromagnetic valve control system for an internal combustion engine as its subject. A similar embodiment of an electromagnetic valve control is known from EP 0 471 614 A1. In these embodiments, the valve is moved back and forth to different positions by electromagnetic force. The electromagnets are disposed inside a housing part of the cylinder head, in two different regions. By the alternating activation of the electromagnets, the valve is moved alternatingly into two terminal positions, corresponding to the opening and closing positions of the valve, respectively. In these terminal positions of the valve, the admission opening for the fuel-air mixture into the combustion chamber is then opened to the widest extent or completely closed.
Another embodiment is known from EP 0 551 271 B1. This embodiment involves a valve mechanism with a plate valve, which is disposed in a passage of an internal combustion engine. The fundamental principle of this embodiment is that the valve plate is divided into two parts; one half of the valve plate executes only a fraction of the stroke executed by the other half of the valve plate.
In these known embodiments for valve control, the major effort of production and assembly of the valve mechanism, because of its complicated design, is especially disadvantageous. This adversely affects the costs for production and assembly. Moreover, in these embodiments, extremely high speeds and strong forces for valve control are necessary, so that an increased vulnerability to malfunction of the valve control from major wear of the parts of the valve mechanism is unavoidable.